1. Field of the Invention
The present invention relates to a thin film magnetic head, a magnetic recording device using the same and a method for manufacturing the same, and particularly to improvement of a thin film magnetic head.
2. Discussion of Background
In recent years, the improvement in performance of a thin film magnetic head is demanded with the improvement in areal recording density of a hard disk device. A thin film magnetic head is composed of a layered structure of a write element for writing and a read element utilizing a magnetoresistance effect for reading. Particularly, recent GMR heads are close to exceed 150 to 200 (GB/P) in areal recording density. A GMR film is of a multilayer structure having a plurality of layers combined with one another. There are some kinds of mechanisms for generating GMR, and the layered structure of a GMR film varies according to the mechanism. As a GMR film for mass production, there are known a spin valve film (hereinafter, referred to as an SV film) and a ferromagnetic tunnel junction film (hereinafter, referred to as a TMR film).
On the other hand, with the improvement in performance of a read element, the improvement in performance of a write element also is demanded. In order to improve a write element in recording density, it is necessary to achieve a narrow track structure, which provides an increased track density. As a means for achieving a narrow track structure, there is known a technique of applying a submicron process onto an upper pole by a semiconductor process technology. However, if the track width is reduced by a semiconductor process technology, difficulty in obtaining a sufficient write magnetic flux arises. To compensate for this disadvantage, a high saturation magnetic flux material (hereinafter, referred to as a HiBs material) is usually used for a narrow track pole.
And in case of a thin film magnetic head for a notebook-sized personal computer, a desktop personal computer, or a high frequency type computer often used as a server or a workstation, excellent high-frequency response characteristic is required. And in a recent hard disk drive, greater access speed is required, and in order to meet the requirement for speed, a compact thin-film magnetic head is required.
The high-frequency characteristic can be improved by shortening the yoke length from a back gap to a pole. Combination of shortening the yoke length YL and using a HiBs material for a pole makes it possible to keep high levels in NLTS, an over-write characteristic (hereinafter, referred to as an O/W characteristic) or the like up to a high-frequency band (500 MHz to 1000 MHz).
Various kinds of techniques for shortening the yoke length are conceivable. One technique is to make a coil pitch as narrow as possible. However, this technique has the following problems.
First, if the coil pitch is narrowed, the coil decreases in width and increases in resistance. As a result, the coil generates heat and the heat raises thermal expansion in the periphery of a pole, namely, thermal protrusion of pole. Since the thermal protrusion causes the possibility of collision between a magnetic head and a recording medium, the thermal protrusion hinders the reduction in floating height of a slider indispensable for high-density recording. Therefore, a technique of shortening the yoke length by narrowing the coil pitch has a limit.
Next, with the advance of narrowing the coil pitch, a photolithography process for forming a coil becomes more difficult. The reason is that the narrower the coil pitch is, the worse the reflection in exposure affects a photolithography process for forming the coil. Unless some prevention of the reflection is taken, it is impossible to form an accurate and vertical coil. For example, in cases where a coil of 1.5 μm or more in coil height and 0.3 to 0.5 μm in coil pitch is formed by means of an existing photolithography technique, the yield rate remarkably lowers.
Another technique for shortening the yoke length YL is to reduce the number of coil turns. In this case, the resistance of coil can be reduced by increasing the height of coil. However, since this method reduces the number of coil turns, it cannot provide a sufficient write magnetic flux and causes a defective O/W characteristic. And it is very difficult to make high a coil having a narrow coil pitch and particularly, when the coil is formed by plating and then a seed layer is etched by ion beams, short-circuiting between the coil turns occurs frequently.
Generally, a write element of a thin film magnetic head is designed so that the minimum coil width of the coil closest to the air bearing surface (hereinafter, referred to as ABS) determines the yoke length YL. Since the total length of this minimum coil width determines a coil resistance of 60 to 70% or more of the total coil resistance, it is necessary to make the total length of the minimum coil width as short as possible in order to shortening the yoke length YL. If a coil with wide coilturns is used to reduce the coil resistance, the yoke length YL cannot be shortened and such a write element has an inferior high-frequency characteristic, and inferior NLTS and O/W characteristic in a high frequency range, which causes the reduction in yield rate.
A conceivable structure for increasing the coil sectional area (increasing the coil height) to increase the number of coilturns and decrease the coil resistance as keeping the yoke length YL short, is a structure in which coils are stacked in the layered form such as two layers or three layers. However, such a layered structure increases the distance between a write gap film and a GMR sensor and so, it has difficulty in achieving both a narrow GMR height (reader portion) and a narrow throat (write portion) in case of polishing the ABS in the polishing process for forming the slider. In some angles of polishing the slider, the throat height varies greatly.
As a means for improving the high-frequency characteristic of a thin film magnetic head, various prior arts have been proposed up to now. For example, the specification of U.S. Pat. No. 6,043,959 discloses a technique in which a second yoke (upper yoke) is made flat to reduce the mutual inductance of coils and thus improve the high-frequency characteristic. The specification of U.S. Pat. No. 6,259,583B1 discloses a structure in which high-permeability and low-anisotropy layers and non-magnetic layers are alternately stacked to form a second flat yoke.
The flat pole structures as disclosed in the above-mentioned prior arts are defined by photolithography. In order to enhance the recording density in the flat pole structures, it is necessary to apply a submicron process onto the pole portion through a semiconductor processing technique and achieve a narrow-track structure. However, in the submicron process there are the problems described above. The above-mentioned prior arts do not disclose a means for solving those problems.